Lead frame and method for manufacturing same

ABSTRACT

A method for manufacturing a lead frame employing a resist pattern formed on a matrix and having a cavity therein, in which an electro-deposition pattern is formed. A connecting cavity portion interconnects tip ends of inner lead cavity portions such that a connecting portion interconnects the tip ends of inner leads of the electro-deposition pattern formed in the cavity. The connecting piece is maintained while the electro-deposition pattern is separated from the matrix and the resist.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a lead frame adapted to be used for asemiconductor device and a method for manufacturing the same.

2. Description of the Related Art

In general, lead frames for use in semiconductor devices aremanufactured by punching or etching metallic materials.

However, in the case of punching or etching, the minimum processingwidth is approximately the same as the material thickness so that theprocessing range is limited, and there is a limit to forming a finepattern from a material of a predetermined thickness.

On the other hand, as well known, there is provided a method formanufacturing lead frames by means of electro-forming (disclosed inJapanese Examined Patent Publication (Kokoku) No. 48-39867).

This known electro-forming process is shown in FIGS. 7(a), (b), (c), (d)and (e), and will be described below: A resist 11 is coated or adheredon a matrix 10 made of conductive material such as stainless steel, asshown in FIG. 7(a); pattern printing is conducted, as shown in FIG.7(b); developing is conducted so as to form a resist pattern 12, asshown in FIG. 7(c); when this resist pattern is used as a mask, anelectro-deposition pattern 13 is formed on the matrix 10 by means ofplating, as shown in FIG. 7(d); the resist pattern 12 is removed; andfurther the electro-deposition pattern 13 is separated from the matrix10, as shown in FIG. 7(e).

Next, the electro-deposition pattern 13 is subjected to necessaryplating. In this way, a lead frame is manufactured.

In some cases, after the resist pattern 12 has been removed from thematrix 10, a surface of the electro-deposition pattern 13 is ground sothat the thickness of the electro-deposition pattern 13 can be madeuniform.

According to this electro-forming process, a lead frame having a veryfine pattern, the section of which is rectangular, can be accuratelymanufactured.

In the above manufacturing process of lead frames, the followingproblems may be encountered: When the electro-deposition pattern 13 isseparated from the matrix 10 in the electro-forming process, theelectro-deposition pattern 13 may be deformed. Also, theelectro-deposition pattern 13 may be deformed in the processes conductedafter electro-forming, for example, in the process of plating. Further,in the case where the electro-deposition pattern 13 is ground, theelectro-deposition pattern 13 tends to be deformed. Such a deformationof the electro-deposition pattern 13 may become substantial when thepattern is fine.

Also, if the inner lead pattern becomes finer, the resist pattern 12 forthe mask must become finer and, therefore, the electro-depositionpattern 13 must be developed in narrow recesses of the resist pattern12. When electro-forming is conducted, hydrogen is generated due to anegative pole reaction. If the resist pattern 12 is narrow as mentionedabove, the hydrogen particles in small bubbles will be attached to theinner walls of the resist pattern 12 because the plating liquid does notflow smoothly. Therefore, a good plated film is not formed, since smallpits or holes are formed in the electro-deposition pattern 13.

SUMMARY OF THE INVENTION

The present invention has been developed to solve the above problems. Itis an object of the present invention to provide a method formanufacturing a lead frame by which an electro-deposition pattern is notdeformed in the processes conducted after an electro-forming process,for example, in the process of plating.

In order to solve the above problems, the present invention is providedwith the following construction.

The present invention provides a method for manufacturing a lead framein which a predetermined pattern is formed on a matrix by a resist, anelectro-deposition portion is provided in a cavity formed in the resistpattern, and the electro-deposition pattern is separated from thematrix, said method comprising the steps of forming the resist patternon the matrix so that a cavity portion for connecting tip ends of aplurality of cavities for forming inner leads is included in the resistpattern; providing an electro-deposition portion into the cavity portionas well as said plurality of cavities so that the electro-depositionpattern can be formed into a configuration in which tip ends of theinner leads are connected by a connecting piece; and separating theelectro-deposition pattern from the matrix while the tip ends of theinner leads are connected by the connecting piece.

It is preferable to provide a method for manufacturing a lead framewhich further comprises the steps of: conducting required processesincluding a plating process after the separation of theelectro-deposition pattern while the tip ends of the inner leads areconnected by the connecting piece; and then removing and separating theconnecting piece from said electro-deposition pattern.

According to the above, the electro-deposition pattern is formed so thatthe tip ends of the inner leads can be connected with the connectingpiece. Therefore, deformation of the inner lead can be prevented whenthe electro-deposition pattern is separated from the matrix and alsowhen the electro-deposition pattern is subjected to the processes suchas plating after that. Even when the electro-deposition pattern isground in the electro-forming process, deformation can be prevented tothe utmost since the fore ends of the inner lead are connected by theconnecting piece.

Also, according to the present invention, since there is a recess forthe connecting piece for connecting a plurality of inner leads, theplating liquid flows smoothly and therefore hydrogen generated due tothe negative pole reaction liquid is not attached to the inner walls ofthe resist pattern. Thus, generation of small pits or holes in theelectro-deposition pattern is prevented.

In another aspect of this invention, there is provided a method formanufacturing a lead frame in which a predetermined pattern is formed ona matrix by a resist, an electro-deposition portion is provided in acavity formed in said resist pattern, and said electro-depositionpattern is separated from said matrix, said method comprising the stepsof forming a necessary plated coat on said electro-deposition patternafter said electro-deposition pattern has been formed on said matrix;and then separating said electro-deposition pattern from said matrix.

Since the electro-deposition pattern is subjected to plating before theelectro-deposition pattern is separated from the matrix, the deformationof the electro-deposition pattern can be prevented in a plating process.

In still another aspect of this invention, there is provided a methodfor manufacturing a lead frame in which a predetermined pattern isformed on a matrix by a resist, an electro-deposition portion isprovided in a cavity formed in said resist pattern, and saidelectro-deposition pattern is separated from said matrix, said methodcomprising the steps of removing said resist after saidelectro-deposition pattern has been formed; fixing a portion of saidelectro-deposition pattern corresponding to inner leads in which saidelectro-deposition pattern is dense, with a fixing member; andseparating said electro-deposition pattern from said matrix.

Also, there is provided a method for manufacturing a lead frame in whicha predetermined pattern is formed on a matrix by a resist, anelectro-deposition portion is provided in a cavity formed in said resistpattern, and said electrode-deposition pattern is separated from saidmatrix, said method comprising the steps of removing said resist aftersaid electro-deposition pattern has been formed; providing a dumb bar inbase portions of outer leads of said electro-deposition pattern forpreventing a leakage of resin in the process of molding and also forfixing said outer leads; and separating said electro-deposition patternfrom said matrix while said dumb bar is fixing said outer leads.

Under the condition that the inner leads are fixed by the fixing member,and the outer leads are fixed by the dumb bar, the electro-depositionpattern is separated from the matrix. Therefore, the deformation of theleads can be prevented when the electro-deposition pattern is separatedfrom the matrix.

Also, there is provided a lead frame comprising a predetermined patternwhich is formed by providing a plated coat on a matrix by means ofelectro-forming, characterized in that a stage portion of said leadframe on which a semiconductor element is to be mounted is formedthicker than inner leads by a multi-layer plated coat. Since the stageportion is formed thicker than the inner leads from a multi-layerplating coat, a lead frame having high radiating properties can beobtained. The stage portion may be formed from a multi-layer composed ofplated coats made of different metals. If the stage portion is amulti-layer plating coat made of different metals, a lead frame havingsufficient radiating properties and mechanical strength can be obtained.

There is also provided a lead frame, wherein tip ends of predeterminedinner leads surround a stage portion, and said stage portion isconnected by a thin connecting portion of a plated coat protruded fromthe tip ends of the inner leads and an outer periphery of the stageportion.

If the tip ends of the inner leads for ground connection and the stageportion are connected by a thin connecting portion, and also if a stagesupport bar and the stage portion are connected by the thin connectingportion, the connection can be easily conducted, and an excessive forceis not given in the case of depressing in which the stage portion isdepressed with respect to the inner lead surface. Therefore, thedeformation of the inner leads can be prevented.

A plurality of dimples may be provided on a surface opposite to asurface of said stage portion on which a semiconductor element ismounted, and said dimples are formed in such a manner that the diameterthereof is extended as it advances to the inside from the oppositesurface. If the dimples are formed in the stage portion, adhesion can beimproved with respect to the resin for sealing.

There is also provided a lead frame formed by electro-forming,characterized in that an outer lead of said lead frame is formed into amulti-layer.

The multi-layer portion of said lead frame may be composed of a metalliclayer and a reinforcing layer formed on one side or both sides of saidmetallic layer.

The metallic layer may be made of copper or copper alloy and saidreinforcing layer may be made of iron, nickel or alloy of these metals.

Also, there is provided a method for manufacturing a lead frame byelectro-forming, characterized in that a metallic layer is formed on amatrix in accordance with a pattern of said lead frame and a reinforcinglayer is formed at least on the pattern of an outer lead portion on saidmetallic layer.

Also, there is provided a method for manufacturing a lead frame byelectro-forming, characterized in that a reinforcing layer is formed ona matrix in accordance with at least a pattern of an outer lead portionin a pattern of the lead frame; a metallic layer is formed on saidreinforcing layer in accordance with the pattern of said lead frame; anda reinforcing layer is formed at least on a pattern of the outer leadportion of said metallic layer.

If the main body portion of a lead frame is formed by electro-forming,it is possible to manufacture the lead frame easily when the inner leadsand the like are formed into a very fine pattern. Also, if the main bodyportion of the lead frame is made of copper or copper alloy, a leadframe product excellent in radiating properties and electriccharacteristics can be provided. Since the reinforcing layer is formedin the outer lead portion, a product having mechanical strengthnecessary to allow bending of the lead can be obtained, and a highlyreliable product can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(a) to 1(h) show a process of a first embodiment of the presentinvention;

FIG. 2 is a schematic illustration showing another embodiment of aresist pattern;

FIG. 3 is a schematic illustration showing an example in which a thinportion is formed in a connecting base portion of the inner lead and theconnecting piece;

FIGS. 4(a) and 4(b) are schematic illustrations showing an example inwhich the resist pattern in FIG. 3 is formed;

FIG. 5 is a schematic illustration showing an example of a section of acavity portion for the formation of the inner lead;

FIG. 6 is a sectional view showing another embodiment of the connectingpiece;

FIGS. 7(a) to 7(e) show a process of a conventional method formanufacturing a lead frame;

FIGS. 8(a) to 8(d) show still another embodiment of the presentinvention;

FIGS. 9(a) to 9(c) show still another embodiment of the presentinvention;

FIG. 10 shows an embodiment of the present invention which includes adumb bar;

FIG. 11 is a cross-sectional view of an embodiment of a lead frame ofthe present invention;

FIG. 12 is a plan view of the embodiment of FIG. 11;

FIGS. 13 and 14 show a manufacturing process of the lead frame shown inFIGS. 11 and 12;

FIG. 15 is a view showing another embodiment of a lead frame of thisinvention;

FIG. 16 is a view showing another embodiment of a lead frame of thepresent invention;

FIG. 17 is a schematic illustration of a lead frame of this invention;

FIGS. 18(a) and 18(b) show a method for manufacturing the lead frameshown in FIG. 17; and

FIG. 19 shows another embodiment of a lead frame of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the accompanying drawings, preferred embodiments of thepresent invention will be explained in detail hereafter.

FIGS. 1(a) to 1(h) show the first embodiment of the invention.

The electro-deposition processes shown in FIGS. 1(a), 1(b), 1(c) and1(d) are the same as the conventional electro-deposition processes shownin FIG. 7(a) to 7(d), respectively. Therefore, the explanation of theseprocesses of the electro-deposition will be omitted here.

In order to make the thickness of the deposition pattern 13 uniform, theelectro-deposition pattern 13 is appropriately ground.

As shown in FIG. 1(h), the electro-deposition pattern 13 is formed insuch a manner that the tip ends of inner leads 22 are connected by aconnecting piece 21. In order to form this connecting piece 21, a cavityportion is formed for connecting the tip ends of a plurality of cavitiesfor inner lead formation, and the electro-deposition pattern 13 is alsoprovided in this cavity portion for the connecting piece 21, so that theconnecting piece 21 is formed.

Next, in this embodiment, while the resist pattern 12 is left (i.e.,remains in place), the electro-deposition pattern 13 is subjected tonecessary plating such as silver plating so as to form a plating layer14, as shown in FIG. 1(e).

Next, the resist pattern 12 is removed, as shown in FIG. 1(f). Finally,the electro-deposition pattern 13 is removed from the matrix 10. In thisway, the lead frame is completed, as shown in FIG. 1(g).

After that, in order to make a stage surface (not shown) lower comparedto the inner lead surface, a stage support bar (not shown) is subjectedto depressing formation by which a step is provided on the stage supportbar. Then, after the inner leads 22 are fastened by a tape piece (notshown) to prevent movement, the connecting piece 21 is removed. Theprocesses of depressing, fixing by a tape piece, and removing theconnecting piece 21 may be conducted in an order different from thatdescribed above. That is, the order may be changed in accordance withthe configuration of the lead frame. The above-mentioned stage is usedfor mounting thereon a semiconductor chip.

In this embodiment, the electro-deposition pattern 13 is formed underthe condition that the tip ends of the inner leads 22 are connected withthe connecting piece 21. Accordingly, deformation of the inner leads 22can be prevented, when the surface of the electro-deposition pattern 13is ground, when the electro-deposition pattern 13 is separated from thematrix 10, when the electro-deposition pattern 13 is handled, and in anyprocess after that.

In this embodiment, plating is conducted while the resist pattern 12 isleft (i.e., remains in place), so that the deformation of theelectro-deposition pattern 13 can be prevented, and a plating layer isnot formed on the side of the electro-deposition pattern (i.e., lead) 13of the obtained lead frame, so that a short circuit caused between theleads by the migration and peeling of a plating layer can be prevented.

In this connection, the electro-deposition pattern 13 may be ground tomake the thickness of the electro-deposition pattern 13 uniform afterthe removal of the resist pattern 12, and then the electro-depositionpattern 13 may be subjected to plating. Also, in this case, thedeformation of the electro-deposition pattern 13 can be prevented sincethe electro-deposition pattern 13 is subjected to plating under thecondition that it is supported by the matrix 10.

Further, plating may be conducted after the electro-deposition pattern13 is peeled off from the matrix 10. In this case, since the inner leads22 are connected with the connecting piece 21, the deformation of theinner leads 22 can also be prevented. Due to the foregoing, afterelectro-forming has been completed, the electro-deposition pattern 13 issubjected to plating. Therefore, a conventional plating process of leadframes can be carried out. Therefore, advantageously, it is notnecessary to change the conventional apparatus therefor. Further, afterthe electro-deposition pattern 13 has been peeled off, plating isconducted. Accordingly, it is advantageous that a flat surface which hasbeen closely contacted with the matrix 10 can be used as a wire bondingsurface.

In this connection, in the case of a lead frame in which plating is notrequired at all, of course, the plating process is omitted.

FIG. 2 shows the second embodiment of this invention.

In this embodiment, the resist pattern 12 is formed by leaving a resistportion 18, the height of which is smaller than that of other resistportions, in a boundary between the tip end of a cavity 16 for theformation of the inner lead 22 and a cavity portion 17 for the formationof the connecting piece 21, and plating is carried out on the resistpattern 12.

Due to the foregoing, as illustrated in FIG. 3, electro-depositionportions on the side of the cavity 16 for inner lead formation, and thaton the side of the cavity 17 for connecting piece formation can beconnected in a bridge form astride the resist portion 18 having a lowerthickness. In this way, a thin portion 23 is formed in a connecting baseportion with which the connecting piece 21 of the tip ends of the innerleads 22 are connected.

As the thin portion 23 is formed in the above manner, the connectingpiece 21 can be easily removed. In this case, the connecting piece 21 isremoved after a piece of tape has been stuck on the inner lead 22 to fixthe lead frame.

It is preferable that such a resist portion 18, having a lower (i.e.reduced) thickness, of the resist pattern 12 be formed in the followingmanner.

First, as illustrated in FIG. 4(a), the resist portion 18 having a lowerthickness is formed at a predetermined position. Then, as illustrated inFIG. 4(b), a resist is further coated on the resist portion 18 which hasalready been formed, and then the pattern is plated and developed.

FIG. 5 shows still another embodiment of this invention.

In the resist pattern 12 of this embodiment, a section of the cavity 16for the formation of the inner leads is formed into a trapezoid in whichthe matrix 10 side is wider as illustrated in the drawing.

Due to the foregoing, a section of the inner lead 22 growing in thecavity 16 for the formation of the inner lead is formed into atrapezoid. When a side closely contacting with the matrix 10 side isused as a bonding surface as described above, a wide bonding area can beensured.

In order to form the section of the cavity 16 for the inner leadformation into a trapezoid, the following method is recommended.

In the case of exposure of a negative type resist, it is exposed to abeam of light, the intensity of which is relatively low. Then, theinside is exposed to light less than the surface as illustrated in thedrawing. Due to the foregoing, the grade of sensitization is inclined,so that a tapered surface can be formed in the development as describedabove. Reference numeral 15 denotes a mask.

In order to form a section of the cavity 16 for the formation of theinner lead into a reverse trapezoid, sensitization processing may beconducted opposite to the aforementioned manner. In this case, when agrinding surface side of the electro-deposition pattern 13 is used as abonding surface, a wide bonding area can be ensured.

In this connection, a connecting base portion with which the connectingpiece 21 of the inner lead 22 is connected, may be formed narrow so thatthe connecting piece 21 can be easily removed.

FIG. 6 shows still another embodiment of this invention.

This embodiment shows an example of manufacture of the lead frame havinga stage on which a semiconductor chip is to be mounted. In thisembodiment, electro-deposition is conducted in such a manner that a tipend of the inner lead 22 of the electro-deposition pattern 13 isconnected with a wide connecting piece 25 including a stage 24.

As described above, under the condition that the tip ends of the innerlead 22 are connected with the connecting piece 25, the followingprocesses are carried out in the same manner as described above. Aprocess for peeling the electro-deposition pattern 13 from the matrix; aplating process; a process for fixing the inner lead 22 with a piece oftape; and a process for forming the tip end of the inner lead 22, stagesupport bar, and the stage 24 by means of punching.

Also, in this embodiment, under the condition that the inner leads 22are connected with the connecting piece 25, the inner leads 22 aresubjected to a peeling process for peeling the inner leads 22 from thematrix 10, and a plating process. Therefore, the deformation of theinner leads 22 can be prevented. The connecting portion 25a is removedin the later stage by cutting along the lines 26.

In the above embodiments, as the connecting piece 21 (or 25) is formed,the thickness of the electro-deposition pattern 13 electricallydeposited on the matrix 10 can be also made uniform. That is, the innerlead 22 is narrower compared to the stage. Therefore, when theelectro-deposition pattern 13 is formed by means of plating, theelectric current density is increased, so that the thickness of aplating layer tends to increase compared to other portions. However, asthe connecting piece 21 (or 25) is formed, a portion of the connectingpiece 21 (or 25) acts as a dumb bar, and the concentration of electriccurrent density on the tip ends of the inner lead 22 can be avoided.Therefore, the thickness of the electro-deposition pattern 13 can bemade uniform. As a result, stress generated in the process of platingcan be reduced, and looseness of the inner leads 22 can be prevented.

According to the above-mentioned several embodiments, theelectro-deposition pattern is formed so that the tip ends of the innerlead can be connected with the connecting piece. Therefore, thedeformation of the inner lead can be prevented in an electro-formingprocess and after processes such as plating. Particularly, according tothe above-mentioned embodiments, a flow of the plating liquid can beimproved due to the connecting piece 21, so that the thickness of thetips of the inner leads 22 can be prevented from being diminished.

FIGS. 8(a) to 8(g) show another embodiment of this invention. Thecontinuous processes as shown in FIGS. 1(a) to 1(g) can also be appliedto this embodiment. That is, while the resist pattern 12 is left, theelectro-deposition pattern 13 is subjected to plating, as shown in FIG.8(a), and then the resist pattern 12 is removed, as shown in FIG. 8(b).Alternatively, after the resist pattern 12 has been removed, theelectro-deposition pattern 13 can be subjected to plating.

Next, in this embodiment, the fixing member 31 such as a tape is fixedonto a portion of the electro-deposition pattern 13 where the leads aredense, that is, the fixing member 31 is fixed onto the inner leads, asshown in FIG. 8(c). Next, under the condition that the leads are fixedby the fixing member 31, the electro-deposition pattern 13 is separatedfrom the matrix 10, as shown in FIG. 8(d).

In this embodiment, as the electro-deposition pattern 13 is separatedfrom the matrix 10 under the condition that the portions between theinner leads are fixed by the fixing member 31, the deformation of theinner leads can be prevented when they are separated from the matrix 10or when they are handled after that.

Various materials can be used for the fixing member 31, such as anadhesive tape, a resin sheet, a photosensitive dry film, or a sheet onwhich a resist is coated by means of printing and then dried.

FIGS. 9(a) to 9(c) show a still another embodiment of this invention.

In this embodiment, after the electro-deposition process as shown inFIG. 1(d) has been completed, the resist pattern 12 is removed withoutconducting a plating process, as shown in FIG. 9(a). Next, the innerlead portion is fixed by the fixing member 31, as shown in FIG. 9(b).The electro-deposition pattern 13 is separated from the matrix 10, asshown in FIG. 9(c). After that, plating is performed if necessary. Inthis way, the manufacture of the lead frame is completed.

Also, in this embodiment, the deformation of the inner leads can beeffectively prevented in the case where the electro-deposition pattern13 is separated from the matrix 10 and after that.

In the above embodiment, the fixing member 31 is used only for fixingthe inner leads. However, like a lead frame of what is called an LOC(lead on chip) or a COL (chip on lead) type, the fixing member 31 may bea tape which fixes the inner leads and mounts a semiconductor element.Accordingly, this embodiment can be advantageously applied to LOC or COLtype semiconductor devices.

In this connection, in the embodiments shown in FIGS. 8(a) to 8(d) andFIGS. 9(a) to 9(c), the connecting piece 21 which connects the tip endsof the inner leads is not always necessarily provided.

FIG. 10 shows another embodiment of this invention, in this embodiment,a dumb bar 32 is formed in a base portion of the outer leads.

The dumb bar 32 is provided for the purpose of preventing the leakage ofresin (not shown) from gaps between the outer leads in the case wherethe semiconductor chip or element (not shown) is sealed with resin aftera semiconductor element has been mounted on the lead frame and subjectedto wire-bonding. Therefore, the dumb bar 32 is provided for filling thegaps between the outer leads.

The dumb bar 32 is formed in the same manner as that of the formation ofthe fixing member 31 in the previous embodiment.

That is, after the process of plating, the dumb bar 32 is formed in thebase portion of the outer leads in the same manner as that of the fixingmember 31 in the previous embodiment, shown in FIGS. 8(a) to 8(d).Alternatively, in the same manner as that of the embodiment, shown inFIGS. 9(a) to 9(c), the dumb bar 32 is formed and the electro-depositionpattern 13 is separated from the matrix 10. After that, theelectro-deposition pattern 13 is subjected to plating if necessary.

When the dumb bar 32 is formed in the base portion of the outer leads asdescribed above, the outer lead portion can be fixed by the dumb bar 32in the same manner as that of the aforementioned fixing member 31.Accordingly the deformation of the pattern 13 can be prevented when theelectro-deposition pattern 13 is separated from the matrix 10, or whenthe electro-deposition pattern 13 is handled in the plating processafter the electro-deposition pattern has been separated from the matrix10.

The dumb bar 32 may be formed by means of electro-deposition. It becomesdifficult, however, to trim the dumb bar when the outer leads are formedinto a fine pattern.

When the dumb bar 32 is made of a different insulating member like thisembodiment, it is not necessary to conduct trimming. Since the dumb bar32 is fixed before the separation of the electro-deposition pattern 13,there is no possibility that the electro-deposition pattern is deformedin the formation of the dumb bar.

The dumb bar 32 may be formed in the following manner: As illustrated inFIG. 10, an adhesive tape 33 is pressed against the outer lead baseportion so as to be adhered, so that the adhesive is filled in the gapsbetween the outer leads. Alternatively, a photosensitive resist isfilled in the gaps between the leads of the outer lead base portion bymeans of screen printing, and then the resist is dried and hardened soas to form a dumb bar (not shown).

The dumb bar 32 is formed when the photosensitive resist is filled inthe gaps between the leads closed by the matrix 10. Therefore, itbecomes easy to fill the gaps with the photosensitive resist. However,it is necessary to use a dumb bar 32, the separability of which is highwith respect to the matrix 10. For this reason, as illustrated in FIG.10, it is preferable to provide a coating 34, the separability of whichis high, on a portion of the matrix 10 corresponding to the dumb bar 32.

In the above embodiments, the fixing member 31 and the dumb bar 32 areseparately provided. However, it is a matter of course that both thefixing member 31, for fixing the inner lead portion, and the dumb bar32, for fixing the outer leads, are provided. When both the inner leadsand the outer leads are fixed, the deformation can be more effectivelyprevented in the separation from the matrix 10 and in the process ofplating.

In the above embodiments, in the case where the electro-depositionpattern 13 is subjected to plating after it has been separated from thematrix 10, it is preferable that a flat surface of theelectro-deposition pattern 13 on the matrix 10 side is formed into abonding surface.

FIG. 11 is a sectional view showing an embodiment of the lead frame 40according to the present invention, and FIG. 12 is a partial plan viewof the same.

The lead frame 40 is manufactured by means of electro-forming asdescribed later, that is, the lead frame 40 is manufactured by forming aplated layer having a predetermined pattern on a matrix by plating.

Numeral 42 is a rail portion, numeral 44 is an outer lead, numeral 46 isan inner lead, and numeral 48 is a stage portion.

In this connection, as shown in FIG. 12, the stage portion 48 may beconnected with an inner lead 46a used as the ground lead among the innerleads 46, through a connecting portion 46b. Alternatively, the stageportion 48 may be connected with a stage support bar, although notillustrated in the drawing.

This embodiment is characterized in that: the rail portion 42 and thestage portion 48 are formed thicker than the inner lead 46 from amulti-layer plating coat.

In the example shown in the drawing, the rail portion 42 is composed ofa first layer 42a connected with the outer lead 44 and the inner lead46, and a second layer 42b formed on the first layer 42a.

In the same manner, the stage portion 48 is composed of a first layer48a connected with the inner lead 46 through a connecting portion, and asecond layer 48b formed on this first layer 48a.

From the viewpoint of mechanical strength, it is preferable that thefirst layer 42a, outer lead 44, inner lead 46 and first layer 48a arepreferably composed of a plating coat made of nickel-cobalt alloy.

In order to improve the thermal radiating properties of the stageportion 48, it is preferable that the second layers 42b and 48b becomposed of a plated coat made of copper.

It is preferable that the multi-layer is made of different metals asdescribed above, however, the multi-layer may be made of the same metal.The number of layers is not limited to two. If necessary, the number oflayers may be three or more.

The purpose of forming the rail portion 42 to be thick is to increasethe mechanical strength of the outer lead 44. On the other hand, theouter lead 44 and the inner lead 46 are formed thin, especially theinner lead 46. Therefore, a fine pattern can be made.

Further, even in a lead frame having no stage, such as a lead frame foran LOC (lead on chip) or a COL (chip on lead) type semiconductor device,the rail portion may be formed thick, or the outer lead may be formedthick.

FIGS. 13 and 14 are views showing the manufacturing process of the leadframe 40 shown in FIGS. 11 and 12.

First, a resist is coated on the matrix 52, exposed to light and thendeveloped, so that a predetermined resist pattern 54 is formed. Next, anickel-cobalt alloy is plated on the matrix 52 by an electro-formingprocess known in the prior art. In this way, the first layer is formedwhich includes the first layer 42a of the rail portion 42, the outerlead 44, the inner lead 46, and the first layer 48a of the stage portion48. At this time, the first layer 48a of the stage portion 48 isconnected with the inner lead 46a by the connecting portion 46b.

When necessary, the layer formed in the aforementioned manner is groundby any mechanical means.

Next, as illustrated in FIG. 14, a resist is coated on the pattern ofthe first layer formed in the aforementioned manner. Then the resist isexposed to light and developed so that a resist pattern 56 is formed forthe aforementioned second layers 42b and 48b. Using such a pattern 56,copper is plated so that the second layers 42b and 48b are formed.

Of course, the plating metal of the first and second layers are notlimited to the specific materials described above.

In this case, if a pattern for forming the second layer 48b of the stageportion 48 is made a little wider than the first layer 48a, the secondlayer 48b is formed in such a manner that the second layer 48b isprotrudes a little from the outer periphery of the first layer 48a asclearly shown in FIG. 14. Due to the foregoing, in the case of resinsealing, the protruding portion enters into the sealing resin, so thatthe adhesion between the stage portion 48 and the sealing resin can beimproved. Further, the heat conduction area can be extended and thethermal radiating properties can be improved.

Next, the resist is removed with an alkali water solution, and finallythe lead frame is peeled off from the matrix 52. In this way, thedesired lead frame 40 can be obtained.

When the lead frame 40 is peeled off from the matrix 52, it ispreferable that an electrically insulating tape is adhered to the innerlead 46 so that the thin inner lead 46 is not deformed.

Since a surface of the stage portion 48 on the matrix 52 side is amirror (flat) surface, a semiconductor element may be mounted on themirror surface side.

FIG. 15 is a view showing another embodiment of this invention.

In this embodiment, when the second layer 48b is formed, a resist layeris formed on the first layer 48a of the stage portion 48, and the resistlayer is exposed and developed, so that a resist pattern 56 having alarge number of holes can be formed as illustrated in the drawing. It ispreferable that the closer to the outer surface the hole is positioned,the larger the diameter of the hole becomes.

In this way, the second layer 48b is formed on the first layer 48a. Whenthe resist pattern 56 is removed, a large number of dimples are formedin the second layer 48b, in which the diameter of the dimples becomeslarger inside the layer from which the resist pattern 56 has beenremoved.

In this way, a large number of dimples are formed in the second layer48b. Accordingly, when a semiconductor element is mounted on the stageportion 48 and sealed by resin together with the stage portion 48, thesealing resin enters the dimples, so that the stage portion 48 can beclosely contacted with the resin.

Although not illustrated in the drawings, even when the second layer 48bof the stage portion 48 is made of the same metal as that of the firstlayer 48a, or the crystal structure is different and the coated surfaceis made rough, the sealing properties can be improved with respect tothe sealing resin.

FIG. 16 is a view showing another embodiment of this invention.

In this embodiment, when the first layer is formed, the tip end of theinner lead 46 (used for ground) and the first layer 48a of the stageportion 48 are not connected by the connecting section 46b, but thefirst layer 48a is completely separate from the inner lead 46.

Next, the resist pattern 56 is formed in a portion except for the firstlayer 48a of the stage portion 48 and a tip end of the inner lead 46a,and plating is conducted to form the second layer.

Then a plated coat is formed on the tip end of the inner lead 46a, andthe first layer 48a of the stage portion 48. As this plated coat grows,it covers the resist 54 between the tip end of the inner lead 46a andthe first layer 48a. As a result, the tip end of the inner lead 46a andthe first layer 48a are connected by the connecting portion 47, theconfiguration of which is formed in such a manner that the center isthin as illustrated in the drawing.

In this way, the lead frame 40 can be obtained, in which the tip end ofthe inner lead 46a and the second layer 48b of the stage portion 48 areconnected by the thin connecting portion 47.

According to the lead frame 40 of this embodiment, the stage portion 48is connected with the inner lead 46 through the thin connecting portion47. Therefore, the deformation of the inner lead 46a can be prevented ina depressing process in which the stage portion 48 is depressed withrespect to the surface of inner lead 46. Although not shown in thedrawings, of course, the stage support bar and the stage portion 48 maybe connected by a connecting portion in the same manner.

FIG. 17 is a schematic illustration showing another embodiment of thelead frame according to the present invention. In FIG. 17, asemiconductor chip 60 is mounted on the lead frame.

In this embodiment, the entire lead frame is manufactured by means ofelectro-forming. The main body of the lead frame including a die pad 62,inner lead 64, outer lead 66 and the like is made of copper or copperalloy, and a reinforcing layer 68 is coated on the outer lead portion66.

The main body of the lead frame is made of copper material as describedabove for the purpose of providing excellent thermal radiatingproperties and electric characteristics to the lead frame. Thereinforcing layer 68 is provided in the outer lead portion 66 for thepurpose of obtaining a predetermined mechanical strength.

With respect to the inner lead portion 64, it is required to form a finepattern, but mechanical strength is not so important. On the other hand,with respect to the outer lead portion 66, it is required to provide apredetermined mechanical strength in order to conduct lead forming.

FIGS. 18(a) and 18(b) show views for illustrating a method formanufacturing the aforementioned lead frame by means of electro-forming.

A main body of the lead frame is obtained when electro-forming isconducted on the matrix 70 with a predetermined pattern, and after that,the formed lead frame is peeled off from the matrix 70. Therefore,first, a resist pattern 72 is formed on the matrix 70 in accordance withthe predetermined patterns of the die pad 62, inner lead 64, outer lead66 and the like. The resist pattern 72 can be formed when a resist iscoated on the matrix 70 and exposed to light and developed using apredetermined pattern.

Next, a metallic layer is formed on the matrix 70 from copper material,wherein the matrix 70 is used for an electrode. Due to the foregoing,the die pad 62, inner lead 64 and the like are made of copper material,as shown in FIG. 18(a).

According to the method for forming a lead frame by means ofelectro-forming, the inner lead 64 and others are formed in accordancewith the resist pattern 72 formed on the matrix 60. Therefore, theaccuracy of the lead frame pattern is determined by the accuracy offormation of the resist pattern 72. Accordingly, even a lead framehaving a fine pitch can be manufactured very accurately.

The electro-forming method is advantageous in that the accuracy is notaffected by the thickness of the lead frame member.

After the die pad 62, inner lead 64 and others have been formed byelectro-forming in the manner described above, the die pad 62 and theinner lead 64 are covered with the resist 74 as shown in FIG. 18(b), andthe outer lead 66 portion is further subjected to electro-forming.

In the case where the outer lead 66 portion is subjected toelectro-forming, a resist pattern may be formed again in the outer leadportion when the coat of the resist 74 is formed. Alternatively, aresist pattern may be used which was provided when the metallic layerwas previously formed from copper material.

In this case, the outer lead 66 portion is subjected to electro-formingusing a material selected from nickel, iron and the like, the mechanicalstrength of which is high. In this way, the reinforcing layer 68 can beformed on the outer lead 66 portion.

After the reinforcing layer 68 has been provided on the outer lead 66 inthe manner described above, the unnecessary resist 74 is removed and thelead frame is peeled off from the matrix 70. In this way, a lead frameproduct can be obtained.

In the obtained lead frame product, the die pad 62, inner lead 64 andouter lead 66 are formed from copper material. Further, the outer lead66 portion is covered with the reinforcing layer 68 made of nickel oriron. Accordingly, a lead frame product can be obtained, in which thedie pad 62 portion and the outer lead 66 portion are provided withexcellent radiating properties and further the electric characteristicsof the lead frame product are excellent. In this lead frame product, theouter lead 66 is provided with a predetermined mechanical strength, andlead forming can be appropriately carried out, and further thedeformation of the lead can be prevented. In this way, a highly reliableproduct can be obtained.

The product of the above embodiment is composed of two layers in such amanner that only one side of the outer lead 66 is coated with thereinforcing layer 68. However, as illustrated in FIG. 19, it is possibleto employ a three layer structure in which the reinforcing layers 68 areprovided on both sides of the outer lead 66. When the three layerstructure is adopted in the manner described above, the reinforcingeffect of the outer lead 66 is further improved.

In the case where the three layer structure is adopted, the reinforcinglayer 68 of the outer lead 66 portion is formed on the matrix 70 bymeans of electro-forming before the main body portion of the lead frameis formed from copper material, and then the main portion of the leadframe is formed, and further the reinforcing layer 68 is formed. In thecase of the three layer structure, a metallic layer on the inner leadportion is formed on the same surface as the reinforcing layer 68 formedin the beginning.

As described above, the order to form the metallic layer on the matrix70 is not specifically limited. In the embodiment shown in FIG. 17, themain body portion of the lead frame may be formed from copper materialafter the reinforcing layer 68 has been subjected to pattern formation.

Also, the reinforcing layer 68 may be made of the same metal as that ofthe metallic layer of the main body of the lead frame.

In the embodiments shown in FIGS. 17 and 19, the die pad 62 portion iscomposed of only one layer made of copper material; however, the die pad62 portion may be composed of two layers, by the reinforcing material,in the same manner as that of the outer lead 66.

In the above embodiments, after the lead frame has been formed on thematrix 70 from copper material and reinforcing material, the lead frameis peeled off from the matrix 70 so as to obtain the product. However,the following method may be employed: For example, an aluminum filmwhich can be easily removed by etching is previously formed on thematrix 70. A lead frame is formed on this aluminum film by means ofelectro-forming in the same manner as that of the above embodiment.After that, the lead frame is peeled off from the matrix 70 with respectto the aluminum film portion, and then the aluminum film is removed bymeans of etching. In this way, the product can be obtained.

In the case where the reinforcing layer 68 is provided on the outer lead66, as illustrated in FIGS. 17 and 19, it is designed so that a portionof the outer lead 66 reinforced by the reinforcing layer 68 canpartially enter the sealing resin. When an end of the reinforcing layer68 partially enters the sealing resin so as to seal the resin,mechanical strength of the lead can be positively maintained in theboundary portion between the sealing resin and the outer lead.Therefore, the formation of the lead can be positively carried out, andthe deformation of the outer lead 66 can be effectively prevented.

With reference to preferred embodiments, the present invention isvariously explained above. However, it should be noted that the presentinvention is not limited to the specific embodiments, and it is a matterof course that such variations, modifications and eliminations of partsmay be made therein within the scope of the appended claims withoutdeparting from the spirit of the invention.

We claim:
 1. A method for manufacturing a lead frame on a major surfaceof a matrix, comprising the steps of:forming a resist pattern on saidmajor surface of said matrix, the resist pattern having therein aconnection cavity connecting tip ends of a plurality of inner leadcavities, the connection cavity and the inner lead cavities having atrapezoidal cross-section in a plane perpendicular to the major surfaceof the matrix and in which the edge of the trapezoid adjacent the majorsurface of the matrix is greater in dimension than the edge of thetrapezoid on the side thereof remote from the major surface of thematrix; forming an electro-deposition pattern in said connection cavityand said plurality of inner lead cavities such that tip ends of innerleads, formed in the inner lead cavities, are connected by a connectingpiece formed in the connection cavity; and separating saidelectro-deposition pattern from said cavities of said resist and fromsaid matrix while the tip ends of said inner leads are connected by saidconnecting piece.
 2. A method for manufacturing a lead frame accordingto claim 1, said method further comprising the steps of:conducting aplating process, after the separation of said electro-deposition patternfrom the matrix but while maintaining the tip ends of said inner leadsconnected by said connecting piece; and removing said connecting piecefrom said inner leads of said electro-deposition pattern.
 3. A methodfor manufacturing a lead frame according to claim 1, further comprisingthe step of providing said resist pattern with a reduced height resistportion, relatively to the height of the remainder of the resistpattern, in respective locations between the tip ends of said inner leadcavities and said connection cavity.
 4. A method for manufacturing alead frame as recited in claim 1, further comprising the steps of:priorto the separating step, forming a plated coat on said electro-depositionpattern after said electro-deposition pattern has been formed on saidmatrix; and then separating said electro-deposition pattern, with saidplated coat formed thereon, from said matrix.
 5. A method formanufacturing a lead frame on a major surface of a matrix, comprisingthe steps of:forming a resist pattern on said major surface of saidmatrix, said resist pattern having a cavity therein corresponding to apattern of the lead frame, the cavity having a trapezoidal cross-sectionin a plane perpendicular to the major surface of the matrix and in whichthe edge of the trapezoid adjacent the major surface of the matrix isgreater in dimension that the edge of the trapezoid on the side thereofremote from the major surface of the matrix; forming anelectro-deposition pattern in said cavity of the resist pattern;removing said resist pattern after said electro-deposition pattern hasbeen formed; fixing a portion of said electro-deposition pattern,corresponding to inner leads and in which said electro-depositionpattern is dense, with a fixing member; and separating saidelectro-deposition pattern from said matrix while maintaining saidfixing member fixed to said portion of said electro-deposition pattern.6. A method for manufacturing a lead frame according to claim 5, whereinsaid fixing member comprises an adhesive tape.
 7. A method formanufacturing a lead frame on a major surface of a matrix, comprisingthe steps of:forming a resist pattern on said major surface of saidmatrix, said resist pattern having a cavity therein corresponding to apattern of the lead frame, the cavity having a trapezoidal cross-sectionin a plane perpendicular to the major surface of the matrix and in whichthe edge of the trapezoid adjacent the major surface of the matrix isgreater in dimension that the edge of the trapezoid on the side thereofremote from the major surface of the matrix; forming anelectro-deposition pattern in said cavity of the resist pattern;removing said resist pattern after said electro-deposition pattern hasbeen formed; providing a dumb bar in base portions of outer leads ofsaid electro-deposition pattern for preventing leakage of resin in theprocess of molding and also for fixing said outer leads; and separatingsaid electro-deposition pattern from said matrix while said outer leadsremain fixed by said dumb bar.